Surface reactions of metal clusters I: The fast flow cluster reactor

Abstract

A new fast flow device for the study of metal cluster reactions in the gas phase is described and characterized. The new device utilizes metal clusters made by laser vaporization of an appropriate metal target mounted in the throat of a supersonic nozzle which exhausts into a fast-flow reaction tube. Reactants are injected into the flowing helium–metal cluster mixture at a point in the flow tube where shock waves have reheated the gas to roughly 320 K. Turbulence in the wake of these shock waves produces efficient mixing of the reactants. Measurement of the flow properties of this reaction tube indicate a residence time of 150–200 μs with an average density of helium buffer gas equivalent to 50–100 Torr at room temperature. Subsequent free expansion of this reaction mixture into a large vacuum chamber produces a supersonic beam with extensive cooling of the various constituents in the mixture (pyrazine was measured to be rotationally cooled to 10 K). The new cluster reaction device is, therefore, an excellent source for future studies of the jet-cooled metal cluster reaction products themselves.